fix: correct LoggerFileBackend API usage to fix Oban startup

The previous commit (90e8964) introduced an incorrect LoggerBackends.add/2
call that prevented Oban from starting, causing all discovery jobs to remain
stuck in "available" state without being processed.

Root cause: LoggerBackends.add expects a tuple {module, id} as the first
argument, not the module alone with configuration options.

Fix: Use the correct API pattern:
1. Add backend with tuple identifier: {LoggerFileBackend, :file_log}
2. Configure separately with Logger.configure_backend/2

This resolves device discovery being completely broken - all background
jobs (discovery, polling, monitoring) now process correctly.

lib/towerops/application.ex

@@ -225,7 +225,11 @@ defmodule Towerops.Application do
   # Register file logger backend for development (only available in :dev environment)
   defp register_file_logger do
     if Code.ensure_loaded?(LoggerBackends) do
-      LoggerBackends.add(LoggerFileBackend,
+      # Add the backend with a unique identifier
+      LoggerBackends.add({LoggerFileBackend, :file_log})
+
+      # Configure the backend with path and level
+      Logger.configure_backend({LoggerFileBackend, :file_log},
         path: "_build/dev.log",
         level: :debug
       )